In this project the prevalence, distribution and ecology of tickborne disease agents, arboviruses, rickettsiae and spiroplasms, are studied. These pathogens are isolated in tissue cultures or laboratory animals from field-collected materials and are serologically identified. If new, pathogens are physicochemically and biologically characterized and taxonomically classified. Of particular importance is the delineation of vector-relationships and human disease potential of the increasing number of tickborne viruses in the United States.